As mobile radio communications techniques typically for cellular phones, a plurality of communication schemes called Third Generation have been adopted as IMT-2000 by the ITU (International Telecommunication Union); among such schemes, commercial services based on W-CDMA (Wideband Code Division Multiple Access) were started in 2001 in Japan.
The W-CDMA was developed for the purpose of obtaining maximum communication speeds around 2 Mbps (bits per second) for each mobile station, and its first version of specifications was defined by Release 99 (Release 1999) provided in 1999 by a standardization organization named 3GPP (3rd Generation Partnership Project).
In communication from a base station to mobile stations in the WCDMA, dedicated physical channels called downlink DPCH (downlink Dedicated Physical Channel) are assigned to individual mobile stations. Data from the higher-layer downlink transport channel DCH (Dedicated Channel) is mapped to the downlink DPCH.
For an expansion of the WCDMA, a communications technique called HSDPA (High speed Downlink Packet Access) is under development. The HSDPA is described in Release 5, Release 6, etc. provided by the standardization organization 3GPP, and its object is to obtain still higher communication speeds (e.g. maximum speed of 14 Mbps).
Compared with the WCDMA, the HSDPA additionally allows the use of physical channels such as the HS-PDSCH (High speed Physical Downlink Shared Channel), the HS-SCCH (HS-DSCH-related Shared Control Channel), and the HS-DPCCH (Dedicated Physical Control Channel (uplink) for HS-DSCH).
The HS-PDSCH is a downlink shared data channel that is used to transmit data from a base station to a mobile station in association with the downlink DPCH from the base station to the mobile station, and the HS-SCCH is a downlink shared control channel used from the base station to the mobile station to transmit control information necessary to receive the HS-PDSCH. The HS-DPCCH is an uplink dedicated control channel used from the mobile station to the base station to transmit information about conditions of the reception of the HS-PDSCH in the mobile station.
Data from the higher-layer transport channel HS-DSCH (High Speed Downlink Shared Channel) is mapped to the physical channel HS-PDSCH. The transport channel HS-DSCH is a downlink transport channel that is shared by a plurality of mobile stations, and the transport channel HS-DSCH is used in association with one downlink DPCH and one or a plurality of HS-SCCHs.
The transport channel HS-DSCH is mapped to one or a plurality of HS-PDSCHs.
Channelization code information about one or a plurality of HS-PDSCHs to which the transport channel HS-DSCH is mapped is included in a HS-SCCH subframe as channelization code set information, and transmitted from the base station to the mobile station. Information about the conditions of reception of the HS-PDSCH in the mobile station is transmitted from the mobile station to the base station by using the dedicated physical control channel HS-DPCCH.
FIGS. 1 to 4 are diagrams respectively illustrating the radio formats for the downlink DPCH, HS-PDSCH, HS-SCCH and HS-DPCCH. Where, the time length of one radio frame is 10 msec, and one radio frame is divided into 15 time slots. The time length of one subframe is 2 msec, and one subframe corresponds to three time slots. One time slot corresponds to 2560 chips of spreading code.
FIG. 1 is a diagram illustrating an example of the radio format for the downlink DPCH. In FIG. 1, the downlink DPCH includes a data channel called downlink DPDCH (Dedicated Physical Data Channel) and/or a control channel called downlink DPCCH (Dedicated Physical Control Channel). The downlink DPCH is a downlink dedicated physical channel individually assigned to mobile stations.
In FIG. 1, Data 1 and Data 2 indicate data mapped from the transport channel DCH to the DPCH, TPC indicates Transmit Power Control information, TFCI indicates Transport Format Combination Indicator, Pilot indicates pilot control information, and slots #0 to #14 are defined by equally dividing one radio frame into 15. One Transmission Time Interval of the DPCH is an integral multiple of 10 msec corresponding to the time length of one frame, for example.
FIG. 2 is a diagram illustrating the radio format for the HS-PDSCH. It is possible to provide a plurality of HS-PDSCHs for one cell of one base station or for one sector, and the individual HS-PDSCHs are code-spread by using different channelization codes. The HS-PDSCH can be shared by a plurality of mobile stations for one base station or one sector.
In FIG. 2, Data indicates data that is mapped to the HS-PDSCH from the transport channel HS-DSCH. One subframe has a time length corresponding to one fifth of one radio frame. Slots #0 to #2 are defined by equally dividing one subframe into three. One transmission time interval of the HS-PDSCH can be 2 msec, corresponding to the time length of one subframe, for example.
It is also possible to perform multi-code transmission by simultaneously utilizing a plurality of HS-PDSCHs for one mobile station in one subframe.
FIG. 3 is a diagram illustrating the radio format for the HS-SCCH. The HS-SCCH is used to transmit information necessary to receive the HS-DSCH. It is possible to provide a plurality of HS-SCCHs for one cell of one base station or for one sector, and the plurality of HS-SCCHs are code-spread by using different channelization codes. One mobile station can simultaneously monitor some of the plurality of HS-SCCHs. Each HS-SCCH transmits, in each subframe, information necessary to receive one or a plurality of HS-PDSCHs for one mobile station.
In FIG. 3, Data indicates information necessary to receive one or a plurality of HS-PDSCHs for one mobile station. One subframe has a time length corresponding to one fifth of one radio frame. Slots #0 to #2 are defined by equally dividing one subframe into three. One transmission time interval of the HS-SCCH can be 2 msec, corresponding to the time length of one subframe, for example.
For instance, one mobile station simultaneously monitors four HS-SCCHs that are spread with different channelization codes, and selects a subframe for that station from among the plurality of subframes transmitted by the four HS-SCCHs. The subframe for that station includes a channelization code set as information about the channelization codes for 15 HS-PDSCHs utilized for that station, and the mobile station receives the 15 HS-PDSCHs for that station on the basis of the channelization code set.
FIG. 4 is a diagram illustrating the radio format for the HS-DPCCH. The HS-DPCCH is used when a mobile station informs a base station about the conditions of reception of the HS-PDSCH. The HS-DPCCH is an uplink dedicated physical channel that is individually assigned to mobile stations.
In FIG. 4, HARQ-ACK indicates an ACK/NAK (Acknowledgement/Negative acknowledgment) signal that corresponds to the conditions of reception of the HS-PDSCH in the mobile station, and CQI indicates Channel-Quality Indication corresponding to the channel quality of the HS-PDSCH that is measured or estimated by the mobile station.
In communication between one base station and one mobile station, the downlink physical channels shown in FIGS. 1 to 3, i.e. the downlink DPCH of FIG. 1, the HS-PDSCH of FIG. 2, and the HS-SCCH of FIG. 3, are code-multiplexed on the same radio frequency.
More specifically, in communication between one base station and one mobile station, the downlink DPCH assigned to that mobile station, all HS-PDSCHs utilized for that mobile station, and all HS-SCCHs monitored by that mobile station, are code-multiplexed on the same radio frequency.
When the WCDMA (HSDPA) communication uses a shared physical channel, such as the HS-PDSCH, to transmit data from one base station to one mobile station, a deterioration of the radio propagation environment at the radio frequency of the shared physical channel deteriorates the throughput of the shared physical channel, and then the data transmission from the base station to the mobile station will be delayed or stopped.
Also, when the communication between one base station and one mobile station uses a dedicated physical channel such as the DPCH and a shared physical channel such as the HS-PDSCH associated with the downlink DPCH, it is necessary to code-multiplex those dedicated and shared physical channels on the same radio frequency; accordingly, a deterioration of the radio propagation environment at the radio frequency of the dedicated physical channel deteriorates the throughputs of the dedicated physical channel and/or the shared physical channel, and then the data transmission from the base station to the mobile station will be delayed or stopped.
Patent Document 1: Japanese Patent Application Laid-Open No. 2003-9240
Non-Patent Document 1: ARIB STD-T64-C.S0002-B Physical Layer Standards for cdma2000 Spread Spectrum Systems 3.1.3.1.1.2
Non-Patent Document 2: 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (Release 6) 3GPP TS25.211 V6.3.0 (2004-12) (http://www.3gpp.org/ftp/Specs/2004-12/Rel-6/25_series/25211-630.zip)
Non-Patent Document 3: 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (Release 6) 3GPP TS25.212 V6.3.0 (2004-12) (http://www.3gpp.org/ftp/Specs/2004-12/Rel-6/25_series/25212-630.zip)
Non-Patent Document 4: 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (Release 6) 3GPP TS25.214 V6.4.0 (2004-12) (http://www.3gpp.org/ftp/Specs/2004-12/Rel-6/25_series/25214-640.zip)
Non-Patent Document 5: 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (Release 6) 3GPP TS25.222 V6.2.0 (2004-12) (http://www.3gpp.org/ftp/Specs/2004-12/Rel-6/25_series/25222-620.zip)